Field of the Invention
The present invention pertains to a valve assembly that can be used in wellbore operations (such as, for example, in oil, gas, water or disposal wells). More particularly, the present invention pertains to a downhole valve assembly that can be used in wellbore operations, such as well intervention and/or hydraulic fracturing operations. More particularly still, the present invention pertains to a downhole flapper valve assembly having a dissolvable or frangible flapper.
Brief Description of the Prior Art
Frequently, it is desirable to install at least one bridge plug, or other anchoring and sealing device, within a wellbore. Such assemblies can be installed for various reasons: to isolate one portion of a wellbore from another, to prevent fluid flow from one portion of a wellbore to another, and/or provide a fluid pressure sealing barrier at a desired location within said wellbore. Such downhole bridge plugs or other anchoring/sealing devices are frequently installed within the central bore of a casing or tubing string, and both grip/anchor and provide a fluid pressure seal against the inner wall of such pipe. In certain applications, such plugs can also be installed within a section of drilled “open hole” (that is, a section of a wellbore that is not cased with pipe).
Conventional bridge plugs typically comprise an anchoring system designed to grip the inner surface of a surrounding wellbore, as well as a sealing system or packing element to form a fluid pressure seal against said inner surface. Some predetermined amount of force is generally required to energize/expand said packing element and actuate said anchoring system. In certain plug assemblies, such force or load can be supplied by pipe weight situated above the bridge plug, or by tensile loading applied from a wellbore surface; such plugs generally must be continually attached to a pipe string during the setting process in order to receive the force required to actuate said anchor system and energize/expand said sealing mechanism. In other cases, such plug assemblies can be conveyed into a wellbore on spooled wireline to a desired location, and actuated using a specially designed plug setting tool.
Conventional bridge plugs are frequently used in connection with hydraulic fracturing (commonly referred to as “fracking”) operations, which generally entails pumping fluid into a wellbore at elevated pressures in order to fracture subterranean rock formations surrounding said wellbore. In many well fracturing operations, a bridge plug or “frac plug” is conveyed to a desired location within a wellbore. Once positioned at a desired location within a wellbore, the frac plug is actuated to secure or anchor said plug in position and prevent axial movement within said wellbore. Thereafter, a setting tool or other device used to set said plug in place can then be removed, leaving the plug securely anchored within the well bore.
Although designs can vary, many frac plugs have a central axial through bore as well as sealing seat on one end. A ball, dart or other object is typically launched or released into the wellbore from the surface or other point above said plug; eventually, said ball/dart/object will reach the plug and land on said seat. Once said ball/dart/object is securely received on said seat, said central through bore is blocked and fluid is prevented from flowing around said ball through said central through bore. With the central through bore of said plug blocked, hydraulic fracturing can be undertaken in up-hole section(s) of the well bore—that is, the portion of the well between the surface and said plug. Additionally, during downhole well intervention operations (that is, operations other than hydraulic fracturing), plugs and valves are periodically used inside a well bore to control, stop or regulate certain well performance variables such as flowrate and pressure.
Conventional bridge plugs typically suffer from a number of significant limitations. Many conventional mechanical bridge plugs are “permanent”, in the sense that they generally cannot be opened or removed from a wellbore after being set without performing complicated and/or expensive downhole milling operations. Although not as “permanent” in design, ball and seat valves can nonetheless be problematic, particularly during cementing and stimulation operations. Cement and stimulation proppant material (such as, for example, “frac sand” used in hydraulic fracturing operations) can negatively affect the sealing function and operation of said valves.
Thus, there is a need for an effective and versatile down-hole bridge plug that can be set at a desired location within a wellbore. The bridge plug should permit isolation of desired portion(s) of a wellbore, while permitting removal and/or opening of said plug when desired.